A joint is used to interconnect or couple two or more pipes of angular, circular or square shape in section when the necessary frames are combined or assembled to built desired planar or solid objects or buildings. The joint is often fixed by means of a screw which is generally excellent for its reliability, releasability and adaptability. Nevertheless such a fastening means is inconvenient and troublesome in operation assembling or disassembling operation of the pipe frames. To avoid such in operation inconvenience in operation, a forced insertion of the connection members of the joint into open ends of the frame pipes is conventionally employed. For example, the joint is provided with two or more tapered connection members each having an external configuration which is similar to an internal configuration of the pipe and adapted to be forcedly inserted into the open ends of the pipes for interconnection thereof as shown in FIG. 1. According to the joint of this type, a rigid contact between the root of the tapered connection member and an internal wall of the pipe may be ensured. However, the rigid connection between the connection member and the pipe is relaxed after a lapse of time, particularly as a result of a continuous vibration applied thereto, since the joint with the tapered connection member is somewhat tilted downwardly as illustrated by the dotted line in FIG. 1.
In order to attain a more stable coupling between the connection member of the joint with the pipe, the tapered end of the connection member is sometimes provided with an expansion or an enlarged terminus of substantially the same size and configuration as the inner diameter and configuration of the pipe so that the connection member is made into rigid contact with the inner wall of the pipe at the two points, namely at the enlarged terminal and the root of the connection member as shown in FIG. 2. However, even according to this, two point contact undesired relaxation still occurs if the pipes intended to be interconnected are made of deformable materials such as plastic or aluminum.
In another conventional connection, a square connection member is inserted into a square pipe and is subsequently turned to obtain rigid contacts between each of the corners of the connection member and each inner side walls of the pipe as shown in FIGS. 3 and 4. This known way is, however, still ineffective in pipe of deformable material such as aluminum alloy.